EP4646031A1

EP4646031A1 - Isolated converter for supplying an led load

Info

Publication number: EP4646031A1
Application number: EP24172910.2A
Authority: EP
Inventors: Miguel Philipp Schneider
Original assignee: Tridonic GmbH and Co KG
Current assignee: Tridonic GmbH and Co KG
Priority date: 2024-04-29
Filing date: 2024-04-29
Publication date: 2025-11-05

Abstract

The invention relates to an isolated converter (10) for supplying an LED load (20). The isolated converter (10) comprises: a galvanic isolation barrier (11) which is arranged between a primary side and a secondary side of the isolated converter (10); a control circuit (12) arranged on the secondary side of the isolated converter (10), wherein the control circuit (12) is configured to operate at least one switch of the isolated converter (10); a voltage-controlled oscillator, VCO (13), arranged on the primary side of the isolated converter (10); and a voltage sensing circuit (14) arranged on the primary side of the isolated converter (10), wherein the voltage sensing circuit (14) is configured to provide a voltage level of a supply voltage to the VCO (13); and wherein the VCO (13) is configured to issue a voltage sensing signal based on the voltage level, wherein the voltage sensing signal is supplied across the galvanic isolation barrier (11) to the control circuit (12).

Description

TECHNICAL FIELD OF THE INVENTION

The invention relates to an isolated converter for supplying an LED load and to a method of operating such an isolated converter.

BACKGROUND OF THE INVENTION

LED drivers with SELV (safety extra low voltage) capabilities have an isolation barrier (so-called SELV barrier) which separates a high-voltage primary side from a low-voltage secondary side of the driver.
The control logic, e.g. a microcontroller, is typically implemented on the primary side of the driver, where it monitors a mains supply voltage and can receive communication signal (e.g., DALI signals). For instance, depending on the status of the mains voltage, the control logic can adapt the operation of the LED driver.
According to the DALI-2 standard, LED drivers should be capable to receive communication signals on their secondary (low-voltage) side. This could be realized by implementing an additional control logic, e.g. an additional microcontroller, on the secondary side. However, implementing such an additional control logic increases the complexity and cost of the driver.

SUMMARY OF THE INVENTION

Thus, it is an objective of the invention to provide an improved isolated converter and an improvised method for operating such an isolated converter, which avoid the above-mentioned disadvantages.
The object of the present invention is achieved by the solution provided in the enclosed independent claims. Advantageous implementations of the present invention are further defined in the dependent claims.
According to a first aspect, the invention relates to an isolated converter for supplying an LED load. The isolated converter comprises: a galvanic isolation barrier which is arranged between a primary side and a secondary side of the isolated converter; a control circuit arranged on the secondary side of the isolated converter, wherein the control circuit is configured to operate at least one switch of the isolated converter; a voltage-controlled oscillator, VCO, arranged on the primary side of the isolated converter; and a voltage sensing circuit arranged on the primary side of the isolated converter, wherein the voltage sensing circuit is configured to provide a voltage level of a supply voltage to the VCO; and wherein the VCO is configured to issue a voltage sensing signal based on the voltage level, wherein the voltage sensing signal is supplied across the galvanic isolation barrier to the control circuit.
This achieves the advantage that information on the supply voltage received on the primary side of the converter can be transmitted to a control circuit on the secondary side of the converter. The control circuit can use this information for controlling the converter, e.g. via the switch.
Thus, an additional primary side control circuit for sensing the supply voltage level might no longer be required, which reduces the cost and complexity of the converter.
The galvanic isolation barrier can be a SELV barrier of the converter, which separates the primary and secondary side. The primary side and the secondary side can be on different electrical potentials.
The isolated converter can be comprised by an LED driver or can form an LED driver. The LED driver can thus be an isolated driver for supplying an LED load.
The at least one switch can be a switch on the secondary side of the converter. Thus, the isolated converter can be a secondary side switched converter.
The control circuit can be implemented by a microcontroller. In particular, the control circuit on the secondary side is connected to the potential of the secondary side.
The voltage sensing circuit can be configured to sense or tap off a supply voltage which is received at the primary side of the converter.
The supply voltage can be an AC or DC supply voltage. For instance, the supply voltage can be a mains voltage or a rectified mains voltage. The supply voltage can also be a DC voltage which is supplied from an energy storage, e.g., in case of a mains failure. The isolated converter can comprise input terminals on its primary side for receiving the supply voltage.
The voltage sensing circuit providing the voltage level of the supply voltage to the VCO may refer to the voltage sensing circuit issuing a voltage signal indicating the voltage level of the supply voltage to the VCO.
The isolated converter can comprise one or more VCOs which receive information on the supply voltage from the voltage sensing circuit and, in response, issue the voltage sensing signal. For instance, the isolated converter comprises one VCO per phase of the supply voltage.
In an embodiment, the VCO is configured to issue the voltage sensing signal with a variable frequency which represents the voltage level of the supply voltage.
For example, the voltage sensing signal is a PWM (pulse width modulation) signal with a frequency that depends on the voltage level of the supply voltage. The frequency of the PWM signal can be dynamically adapted to changes in the voltage level of the supply voltage. The PWM signal can be transmitted across the galvanic isolation barrier to the control circuit.
In an embodiment, the control circuit is configured to operate the at least one switch of the isolated converter based on the voltage sensing signal received from the VCO. This achieves the advantage that a control circuit on the secondary side can control the converter using information on the supply voltage received on the primary side of the converter.
In an embodiment, the at least one converter comprises at least one optocoupler configured to transmit the voltage sensing signal of the VCO across the galvanic isolation barrier. This achieves the advantage that information on the supply voltage can be transmitted via optical coupling across the isolation barrier.
In an embodiment, the at least one converter comprises at least one capacitive element, in particular at least one capacitor, configured to transmit the voltage sensing signal from the VCO across the galvanic isolation barrier. This achieves the advantage that information on the supply voltage can be transmitted via capacitive coupling across the isolation barrier.
In an embodiment, the at least one converter comprises at least one transformer configured to transmit the voltage sensing signal from the VCO across the galvanic isolation barrier. This achieves the advantage that information on the supply voltage can be transmitted via magnetic coupling across the isolation barrier.
In an embodiment, the control circuit comprises a communication interface, in particular a DALI interface, arranged on the secondary side of the isolated converter; wherein the communication interface is configured to receive at least one communication signal and to forward the communication signal to the control circuit. This achieves the advantage that the converter is capable to receive and process communication signals on its secondary side.
For instance, the at least one communication signal received on the secondary side is a signal in accordance with a specific communication standard, in particular a DALI-2 standard.
The control circuit can be configured to operate the at least one switch of the isolated converter further based on the at least one communication signal.
In an embodiment, the control circuit is configured to detect if the supply voltage is an AC or a DC voltage based on the voltage sensing signal.
The control circuit can analyze further properties of the supply voltage, such as frequency (in case of AC) or min/max voltages.
According to a second aspect, the invention relates to a method for supplying a voltage sensing signal from a primary side of an isolated converter to a control circuit arranged on a secondary side of the isolated converter, wherein the control circuit is configured to operate at least one switch of the isolated converter. The method comprising the steps of: providing a voltage level of a supply voltage to a voltage-controlled oscillator, VCO, which is arranged on the primary side of the isolated converter; issuing the voltage sensing signal based on the voltage level by means of the VCO; and supplying the voltage sensing signal across a galvanic isolation barrier, which is arranged between the primary side and the secondary side of the isolated converter, to the control circuit.
In an embodiment, the voltage sensing signal is issued with a determined frequency which represents the voltage level of the supply voltage.
In an embodiment, the control circuit is configured to operate the at least one switch of the isolated converter based on the voltage sensing signal received from the VCO.
In an embodiment, the voltage sensing signal is transmitted across the galvanic isolation barrier by means of optical, capacitive and/or magnetic coupling.
In an embodiment, the method further comprises: detecting if the supply voltage is an AC or a DC voltage based on the voltage sensing signal.
In an embodiment, the method further comprises: receiving at least one communication signal on the secondary side of the isolated converter and forwarding said communication signal to the control circuit.
For example, the at least one communication signal is a signal in accordance with a communication standard, in particular a DALI-2 standard.
For instance, the control circuit is configured to operate the at least one switch of the isolated converter further based on the at least one communication signal.
The method according to the second aspect of the invention can be a method for operating an isolated converter. For instance, the method according to the second aspect of the invention can be carried out by the isolated converter according to the first aspect of the invention.
According to a third aspect, the invention relates to the use of a voltage-controlled oscillator, VCO, to supply a voltage sensing signal from a primary side of an isolated converter according to the first aspect of the invention to a control circuit arranged on a secondary side of the isolated converter.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in the followings together with the figures.

Fig. 1: shows a schematic diagram of an isolated converter according to an embodiment;
Fig. 2: shows a circuit diagram of a voltage-controlled oscillator according to an embodiment;
Fig. 3: shows a schematic diagram of an isolated converter according to an embodiment;
Fig. 4: shows signals in an isolated converter according to an embodiment;
Fig. 5: shows a flow diagram of a method for supplying a voltage sensing signal from a primary side of an isolated converter to a control circuit on its secondary side according to an embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Fig. 1 shows a schematic diagram of an isolated converter 10 for supplying an LED load 20 according to an embodiment.
The isolated converter 10 comprises: a galvanic isolation barrier 11 which is arranged between a primary side and a secondary side of the isolated converter 10; and a control circuit 12 arranged on the secondary side of the isolated converter 10, wherein the control circuit 12 is configured to operate at least one switch of the isolated converter. The isolated converter 10 further comprises: a voltage-controlled oscillator, VCO 13, arranged on the primary side of the isolated converter 10; and a voltage sensing circuit 14 arranged on the primary side of the isolated converter 10, wherein the voltage sensing circuit 14 is configured to provide a voltage level of a supply voltage to the VCO 13; and wherein the VCO 13 is configured to issue a voltage sensing signal based on the voltage level, wherein the voltage sensing signal is supplied across the galvanic isolation barrier 11 to the control circuit 12.
Thus, by means of the voltage sensing signal, information regarding a current (meaning a currently received) supply voltage level on the primary side of the converter 10 can be transmitted to the control circuit 12 on the secondary side (i.e., on the potential of the secondary side) of the converter 10. In this way, a control circuit 12 on the secondary side can use this information, e.g., for controlling the switch.
The supply voltage can be an AC supply voltage or a DC supply voltage. For instance, the supply voltage can be a mains supply voltage, a rectified mains supply voltage or a DC voltage supplied from an energy storage.
The LED load 20 can comprise one or more LED luminaires. Thus, the isolated converter 10 can be an isolated LED converter. The isolated converter can be comprised by an LED driver or can form an LED driver for the LED load.
The galvanic isolation barrier 11 can be a SELV barrier of the converter 10. The galvanic isolation barrier 11 can separate the primary side from the secondary side. The primary side and the secondary side can be on different electrical potentials. For instance, the primary side can be a high-voltage input side of the converter 10, which receives a mains supply voltage, and the secondary side can be a low-voltage output side of the converter 10, which is connected to the Led load 20 and supplies the LED load 20 with an output voltage.
The at least one switch can be a switch on the secondary side of the converter 10, e.g. in the second stage 19. Thus, the isolated converter can be a secondary side switched converter.
The control circuit 12 can be a microcontroller or an ASIC. In particular, the control circuit 12 on the secondary side is connected to the potential of the secondary side.
The voltage sensing circuit 14 can be configured to sense or tap off the supply voltage which is received at the primary side of the converter 10. For instance, the voltage sensing circuit 14 can comprise electrical lines which are connected to the line (L) and neutral (N) conductors on the input side of the converter 10. Optionally, the voltage sensing circuit 14 can also comprise a voltage divider (not shown).
In the example shown in Fig. 1, the voltage sensing circuit 14 is arranged before an exemplary rectifier 17, which is e.g. a bridge rectifier. However, the voltage sensing circuit 14 could also be arranged downstream of the rectifier 17 (e.g., between rectifier 17 and first stage 18) and forward a rectified voltage signal to the VCO 13.
The voltage sensing circuit 14 can provide a voltage signal to the VCO 13 which indicates the voltage level of the supply voltage (e.g., a mains voltage or rectified mains voltage).
An optional EMI (electromagnetic interference) filter 16 can be arranged before the voltage sensing circuit 14 at the input side of the converter 10.
The VCO 13 can comprise a plurality of VCO circuits, e.g. one VCO circuit for each conductor line (L and N).
The VCO 13 can be configured to issue the voltage sensing signal with a variable frequency which represents the voltage level of the supply voltage.
For example, the voltage sensing signal is a PWM (pulse width modulation) signal with a frequency that depends on the voltage level of the supply voltage. This PWM signal can be transmitted across the galvanic isolation barrier 11.
As shown in Fig. 1, the transmission of the voltage sensing signal across the isolation barrier 11 can be carried out by means of at least one optocoupler 15 of the converter 10.
Alternatively, the converter 10 can also comprise at least one capacitive element (e.g., at least one capacitor) or at least one magnetic coupling element (e.g., at least one transformer) to transmit the output signal of the VCO 13 across the galvanic isolation barrier 11.
The control circuit 12 on the secondary side can analyze the variable frequency of the voltage sensing signal and can infer information about the supply voltage (in particular its level) from the frequency.
For instance, the control circuit can be configured to operate the at least one switch of the isolated converter 10 based on the voltage sensing signal received from the VCO.
The control circuit 12 can use the voltage sensing signal to monitor different aspects of the supply voltage. For instance, based on the voltage sensing signal, the control circuit 12 can detect if the supply voltage is an AC voltage (e.g., a "normal" mains voltage) or a DC voltage (e.g., in case of an emergency operation in the even to of a power failure, where the DC voltage is supplied from a battery) . In the former case (AC voltage), the control circuit 12 can analyze the frequency and/or the max/min voltage of the mains voltage. In the latter case (DC voltage), the control circuit 12 can detect if the DC signal is a constant or a pulsed DC signal.
Depending on which type of supply voltage is provided (AC or DC), the control circuit 12 can control the isolated converter 10 or more specifically the LED driver which comprises the isolated converter 10 in different ways. For instance, in an emergency mode, the control circuit 12 can dim the LED driver to a lower brightness level. When the voltage level of the supply voltage exceeds a threshold, the control circuit 12 can power off the LED driver. In case the supply voltage is a mains supply voltage, the control circuit 12 can control the LED driver to operate in a normal operating mode.
Fig. 2 shows a circuit diagram of the voltage-controlled oscillator (VCO) 13 according to an embodiment.
The VCO 13 can be an oscillator with an oscillation frequency that depends on the voltage level of an input voltage signal. The input voltage signal can be the signal which is supplied to the VCO 13 by the voltage sensing circuit 14, and which indicates the (current) voltage level of the supply voltage.
The exemplary VCO 13 in Fig. 2 comprises two capacitors which are charged by the input voltage (e.g., the voltage signal provided by the voltage sensing circuit 14) via a number of resistors. As a result of said charging, the voltage at the base of two transistors T1 and T2 changes, wherein T1 and T2 feature specific base emitter voltages U_BE. Once U_BE of a transistor is reached, the transistor becomes conducting, allowing one of the capacitors to discharge. This happens periodically with both transistors/capacitors resulting in an oscillating signal with a certain operating frequency that depend on the input voltage.
The VCO 13 design in Fig. 2 is only an example and other VCO circuits could be used in the converter 10, e.g. based on a bistable multivibrator or flip-flop.
Such VCO circuits have the advantage of being relatively cost efficient and simple to implement in a converter 10, and at the same time offer a high precision in mapping the input voltage to a frequency.
Fig. 3 shows a schematic diagram of the isolated converter 10 according to an embodiment.
The isolated converter 10 comprises two VCOs 13, wherein one VCO 13 is connected to the N conductor and one VCO 13 is connected to the L conductor line of the converter 10. Each VCO 13 is coupled to the control unit 12 across the galvanic isolation barrier 11 via a respective optocoupler 15. In this way, the control unit 12 on the secondary side can monitor the voltage across the N and L conductors on the primary side.
Optionally, the control circuit comprises a communication interface 31 on the secondary side of the isolated converter 10. The communication interface can be configured to receive at least one communication signal and to forward the at least one communication signal to the control circuit 12 on the secondary side.
For instance, the communication interface 31 can be a DALI interface. For instance, the communication interface 31 is connected to a DALI bus. The communication signal can be a signal according to a DALI, in particular a DALI-2, communication standard.
By means of the communication interface 31, the converter 10 can receive information on a number of operating parameters of the LED load and/or of other building technology devices, such as sensors or further luminaires in a system. For instance, the information can comprise performance data, failure flags, luminaire operation information, timer data and/or energy reporting.
The control circuit 12 could adapt an operation of the converter 10 based on the received control signal.
Fig. 4 shows signals in the isolated converter 10 according to an embodiment.
The top diagram in Fig. 4 shows the supply voltage received on the primary side of the converter 10. In this case, the supply voltage is an AC voltage whose voltage level gradually changes over time.
The middle diagram in Fig. 4 shows the corresponding voltage sensing signal as provided by the VCO 13. This signal is a PWM signal whose frequency changes dynamically with the voltage level of the supply voltage.
The bottom diagram in Fig. 4 shows the signal at the output of the optocoupler 15 which is provided to the control circuit 12.
Fig. 5 shows a flow diagram of a method 50 for supplying a voltage sensing signal from a primary side of an isolated converter to a control circuit on its secondary side according to an embodiment. For instance, the method can be carried out with the isolated converter 10 as e.g. shown in Figs. 1 or 3.
The method 50 comprises the steps of: providing 51 a voltage level of a supply voltage to a voltage-controlled oscillator, VCO, which is arranged on the primary side of the isolated converter; issuing 52 the voltage sensing signal based on the voltage level by means of the VCO; and supplying 53 the voltage sensing signal across a galvanic isolation barrier, which is arranged between the primary side and the secondary side of the isolated converter, to the control circuit.
The supply voltage can be a mains voltage or a rectified mains voltage. In certain circumstances (e.g., after a mains failure), the supply voltage can also be a DC voltage.
The voltage sensing signal can be issued with a variable frequency which represents the current (meaning currently present) voltage level of the supply voltage.
For example, the control circuit is configured to operate the at least one switch of the isolated converter based on the voltage sensing signal received from the VCO.
The voltage sensing signal can be supplied 53 across the galvanic isolation barrier by means of optical, capacitive and/or magnetic coupling.
In addition, the method 50 can comprise the step of: detecting 54 if the supply voltage is an AC or a DC voltage based on the voltage sensing signal.
The method 50 can comprise the further step of: receiving 55 at least one communication signal on the secondary side of the isolated converter and forwarding said communication signal to the control circuit 12. For instance, the control circuit is configured to operate the at least one switch of the isolated converter further based on the at least one communication signal. The communication signal can be a DALI signal.
Although the invention has been illustrated and described with respect to one or more implementations, equivalent alternations and modifications will occur to those skilled in the art upon the reading of the understanding of the specification and the annexed drawings. In addition, while a particular feature of the invention may have been disclosed with respect to only of the several implementations, such features may be combined with one or more other features of the other implementations as may be desired and advantage for any given or particular application.

Claims

An isolated converter (10) for supplying an LED load (20), comprising:
a galvanic isolation barrier (11) which is arranged between a primary side and a secondary side of the isolated converter (10);

a control circuit (12) arranged on the secondary side of the isolated converter (10), wherein the control circuit (12) is configured to operate at least one switch of the isolated converter (10);

a voltage-controlled oscillator, VCO (13), arranged on the primary side of the isolated converter (10); and

a voltage sensing circuit (14) arranged on the primary side of the isolated converter (10), wherein the voltage sensing circuit (14) is configured to provide a voltage level of a supply voltage to the VCO (13); and

wherein the VCO (13) is configured to issue a voltage sensing signal based on the voltage level, wherein the voltage sensing signal is supplied across the galvanic isolation barrier (11) to the control circuit (12).
The isolated converter (10) of claim 1,
wherein the VCO (13) is configured to issue the voltage sensing signal with a variable frequency which represents the voltage level of the supply voltage.
The isolated converter (10) of claim 1 or 2,
wherein the control circuit (12) is configured to operate the at least one switch of the isolated converter (10) based on the voltage sensing signal received from the VCO (13).
The isolated converter (10) of any one of the preceding claims, comprising:
at least one optocoupler (15) configured to transmit the voltage sensing signal from the VCO (13) across the galvanic isolation barrier (11).
The isolated converter (10) of any one of the preceding claims, comprising:
at least one capacitive element, in particular a capacitor, configured to transmit the voltage sensing signal from the VCO (13) across the galvanic isolation barrier (11).
The isolated converter (10) of any one of the preceding claims, comprising:
at least one transformer configured to transmit the voltage sensing signal from the VCO (13) across the galvanic isolation barrier (11).
The isolated converter (10) of any one of the preceding claims,
wherein the control circuit (12) is configured to detect if the supply voltage is an AC or a DC voltage based on the voltage sensing signal.
The isolated converter (10) of any one of the preceding claims, further comprising:
a communication interface (31), in particular a DALI interface, arranged on the secondary side of the isolated converter (10);

wherein the communication interface (31) is configured to receive at least one communication signal and to forward the communication signal to the control circuit (12).
A method (50) for supplying a voltage sensing signal from a primary side of an isolated converter (10) to a control circuit (12) arranged on a secondary side of the isolated converter (10), wherein the control circuit (12) is configured to operate at least one switch of the isolated converter, the method (50) comprising the steps of:
providing (51) a voltage level of a supply voltage to a voltage-controlled oscillator, VCO (13), which is arranged on the primary side of the isolated converter (10);

issuing (52) the voltage sensing signal based on the voltage level by means of the VCO (13); and

supplying (53) the voltage sensing signal across a galvanic isolation barrier (11), which is arranged between the primary side and the secondary side of the isolated converter (10), to the control circuit (12).
The method of claim 9,
wherein the voltage sensing signal is issued with a variable frequency which represents the voltage level of the supply voltage.
The method of claim 9 or 10,
wherein the control circuit (12) is configured to operate the at least one switch of the isolated converter (10) based on the voltage sensing signal received from the VCO (13).
The method of any one of claims 9 to 11,
wherein the voltage sensing signal is transmitted across the galvanic isolation barrier (11) by means of optical, capacitive and/or magnetic coupling.
The method of any one of claims 9 to 12, further comprising:
detecting (54) if the supply voltage is an AC or a DC voltage based on the voltage sensing signal.
The method of any one of claims 9 to 13, further comprising:
receiving (55) at least one communication signal on the secondary side of the isolated converter (10) and forwarding the communication signal to the control circuit (12).
Use of a voltage-controlled oscillator, VCO (13), to supply a voltage sensing signal from a primary side of an isolated converter (10) according to any one of claims 1 to 8 to a control circuit (12) arranged on a secondary side of the isolated converter (10).